The present invention relates to a tensioner for a safety belt.
Known safety belt tensioners usually comprise a cylinder, a piston slidably arranged within the cylinder, a traction transfer means which is connected with the piston to transfer the movement of the piston to the safety belt, and a drive which may exert a driving force on the piston to tension the safety belt. Such belt tensioners serve for rapidly winding up, if activated, a possibly existing belt slack, so that the safety belt may fully develop its protective effect for the occupant. In order to keep, in the case of restraint, the stress for the vehicle occupant as little as possible, the safety belt device must be able to absorb as much kinetic energy of the vehicle occupant as possible. For this purpose, what is called force limiters are provided which convert the absorbed energy into plastic deformation. Such a force limiter is realized e.g. in the belt tensioner described in DE 297 18 661. In this case, the piston of the belt tensioner has a conical shape, so that when the piston is pulled back by the traction transfer means it forces rolling elements against the cylinder wall. These elements deform the wall plastically when the piston is pulled back along the previously traveled tensioning distance. However, this kind of force limitation can only function if the belt tensioner was actuated and the piston was moved out of its rest position, so that a distance for deforming the cylinder wall is available. If there was no belt slack at the time of actuation or if the belt tensioner was not actuated at all, the piston therefore still being in the rest position, such means for force limitation will remain ineffective.
Thus, it is the object of this invention to provide a belt tensioner which enables force limitation even in the non-actuated condition and in which the tensioning distance and the distance usable for force limitation are independent of each other.
This object is achieved by a tensioner which comprises a cylinder, a piston which is slidably arranged within the cylinder, and a traction transfer means which is connected with the piston to transfer a movement of the piston to the safety belt. The tensioner further comprises a drive which may exert a driving force on the piston to tension the safety belt. The piston is provided with a deformation element which the traction transfer means engages. On the one hand, the deformation element serves as a connection between the piston and traction transfer means and, on the other hand, it may be deformed plastically by a force acting on the traction transfer means so as to act as a force limiter. The deformation element may fulfill this function irrespective of the position of the piston so as to ensure the force limiting function even if the belt tensioner is not actuated.
Further advantageous designs of the invention will be apparent from the following disclosure.